The invention relates to a handpiece as part of a treatment or working instrument or to a treatment or working device for medical purposes.
Such a handpiece may be, inter alia, a medical or dental treatment instrument or a working instrument for a medical or dental laboratory.
Medical or dental handpieces or treatment instruments differ, inter alia, in the functioning of the tool which they in each case carry and in the functioning of the drive. A tool may be driven by means of rotation, such as is for example the case with a drill, or by means of an axial stroke movement, such as is the case with a file, or also in a combination of these movements. A handpiece having a rotary driven tool can, with appropriate configuration of the tool, also be used for the purpose of transmitting a rotational drive force to rotary parts, for example to tighten or loosen screws present at the treatment site, such as is the case for example with screws of dental prostheses or other body parts.
In DE 197 45 245 A1 there is described a handpiece in combination with a tool for the preparation of a tooth root canal, wit h which the maximum torque which can be transmitted to the tool is limit ed to a particular lesser value. By these means, the tool is protected from overloading resulting from the drive, and damage to the tool or breakage of the tool are avoided. This known handpiece is thus restricted in its range of function or application.
With the handpiece in accordance with the invention the arrangement reducing the torque can be selectively deactivated and activated again by means of a setting device. By these means it is possible to employ the handpiece both for those applications in which the maximum torque value should be reduced and also to employ it for those applications in which the maximum torque value made available by the drive present should be fully exploited. The handpiece in accordance with the invention is thus suitable not only for root canal preparation work but also for normal working and drive operations, such as for example material removing working, or turning and screw working on the human or animal body. It can thus be employed at a medical and/or dental treatment station and also at a technical workstation. The handpiece in accordance with the invention can thus be more effectively put to use not only with regard to its expanded range of application but also in the individual situation, for example when the maximum drive force of the drive present should temporarily be employed. This can for example be the case when, for the purpose of carrying out specific types of work, the danger of damage or breakage of the tool is not present or, for particular reasons, is to be accepted as a risk.
The arrangement for reducing or limiting to a particular torque value can be formed by means of an overload coupling which is preferably arranged in the handpiece, or by means of an electrical control device for controlling the electrical drive current for an associated electric motor.
For a handpiece of the kind under consideration there are two significant required features. On the one hand it should be readily operable, so that the operating person can pay more attention to the work to be carried out with the handpiece. On the other hand, the size of a handpiece is subject to restriction, because in the working of the human or animal body it must be put to use in many cases in body cavities, such as is for example the case with the mouth in a dental application. There thus exists the requirement on the one hand to manufacture the handpiece with dimensions as small as possible and on the other hand to ensure a simple and ready operation of the treatment instrument. A particularly advantageous configuration distinguishes itself in that a common setting member is provided both for the overload coupling and also for the direct coupling. By these means there is achieved not only a lesser number of components and thus also a lesser size, but also a simple and ready operation is possible because the operating person must actuate only one setting member. Thereby it is advantageous to so divide the range of movement of the setting member that in one range of movement the maximum transmissible torque can be set and in a second range of movement, joining on the first range of movement, the direct coupling can be engaged and disengaged. An advantageous place for the setting member is located on the outer surface of the treatment instrument, whereby a direction of movement for the setting member directed in the circumferential direction is excellently suited.
In order to avoid an unintended displacement of the setting member, it is advantageous to releasably position the setting member in each setting disposition, by means of a positioning device. For this purpose there is suited a preferably elastically yielding and thus manually overcomable positioning device, which makes it possible in a ready manner to overcome the positioning device concerned with a certain exercise of force. By these means special manual manipulations for releasing the positioning device are avoided.
If, with a treatment instrument of the kind under consideration, the overload coupling comes into function at an increased working resistance and the maximum transmittable torque is thereby restricted in that the mechanical overload coupling races or slips, there is a danger of a non-uniform transmittal of torque during the slippage, which arises in that the rotational engagement between the two coupling parts occurs erratically. This leads, despite to the slippage of the overload coupling, to sudden and repeated torque loading peaks. By these means there arises not only the danger that the tool will be overloaded due to the short term loading peaks, as a form of stick-slip effect, but also that the work being carried out will be adversely affected.
With an overload coupling having, in the circumferential direction, equally long coupling projections and coupling recesses, or shorter coupling recesses, on the mutually facing sides of the coupling disks, see for example FIGS. 6 to 8 in DE 197 45 245 A1, there is a danger that after a disengagement resulting from an overload, as a consequence of the inertia of the parts the arresting moment is initially relatively strong and then strongly reduced in an undesired manner. With the configuration according to FIG. 7 of that document, although the coupling projections bounding the coupling recesses have inclined flanks, whereby the rotational engagement in the case of slippage occurs in a less percussive manner and thus softer, there exists however in this configuration the danger that the coupling elements, preferably formed by means of balls, upon slippage of the overload coupling, spring over the respective following coupling recess and reach the then following coupling projection, whereby the transmitted torque is relatively slight.
It is thus further the object of the invention to reduce the negative influence of inertia on the functioning of the overload coupling.
With a treatment instrument according to claim 15 the coupling projections are shorter in the circumferential direction than the coupling recesses. By these means, in functional operation, the coupling elements have more time to again enter into the associated coupling recesses and upon bearing on the then respectively following coupling projection to maintain the torque transmission. Thereby, upon slippage, there is effected a satisfactory torque transmission at the desired level of the torque.
This advantageous function can, by means of further developments of the invention, be stabilised and attained also for greater ranges of speed of rotation. The further developments also contribute to ensuring a slippage of the overload coupling even with slight variation of the torque. By these means there are avoided in particular suddenly increasing torque values and thus the loading on the tool is reduced. Suddenly changing torque values are in particular disadvantageous with such tools as are sensitive and tend to break, as is the case with tools for the preparation of a root canal of a tooth.
There is thus effected, in functional operation, a softer slippage of the overload coupling, with reduced torque fall-off, by means of which the above-described loading peaks are avoided or at least reduced. With the configuration in accordance with the invention it is equally advantageous whether the rearward or the forward coupling part manifests the characterising features of the invention.
Features disclosed herein contribute the attainment of the object of the invention and lead to simple, economically manufacturable and simply and rapidly installable or disinstallable configurations, whereby a good functioning is ensured and small manufacturing costs are attained.